Liquefaction and separation of air components



y 1966 J. K. LA FLEUR 3,258,929

LIQUEFACTION AND SEPARATION OF AIR COMPONENTS Filed April 18, 1963 BYfMW United States Patent 3,258,929 LIQUEFACTION AND SEPARATION OF AIRCOMPONENTS James K. La Fleur, Hermosa Beach, Calif., assignor to The LaFleur Corporation, Torrance, Caliii, a corporation of California FiledApr. 18, 1963, Ser. No. 273,883 8 Claims. (Cl. 62-22) The presentinvention relates to the construction and arrangement of two rectifiercolumns usable for the liquefaction and substantially completeseparation of the air components oxygen, argon, and nitrogen, and toprocesses for operating such columns and for achieving such liquefactionand separation, such columns to be operated at and such liquefaction andseparation to take place at substantially atmospheric pressure.

Most of the advances in the prior art of air liquefaction and separationof the components oxygen, argon, and nitrogen have been those ofpressure reduction. The prior art does not disclose the liquefaction andcomplete separation at substantially atmospheric pressure of the aircomponents oxygen, argon, and nitrogen. Further, the art does notdisclose such separation being accomplished in only two rectifiercolumns.

The problems of the prior art have not been due to an absence ofadequate refrigeration 'but due to an improper use of that refrigerationavailable. The disclosure of the present invention presupposes means forachieving the desired and needed refrigeration. This refrigeration ispreferably a gas having a critical temperature below that of nitrogen asit is desired torectify in both columns at atmospheric pressure.Further, it is presumed that the needed amount of refrigeration isavailable. While the refrigeration must be adequate, the presentinvention makes a highly economical use of it so that the refrigerationused is at a minimum.

Thus, it is an object of the present invention to liquefy and separatethe air components oxygen, argon, and nitrogen at substantiallyatmospheric pressure and by the use of only two rectifier columns.

Another object is that of constructing such rectifier columns so that ineach column reflux may be accumulated and its rate of delivery to theplates may be controlled.

A further object of the invention is that of separating the componentsof air in only two columns so as to obtain oxygen, argon, and nitrogenwith individual purities of better than 99.5 percent.

The above mentioned defects of the prior art are remedied and theseobjects achieved by a process and apparatus for the liquefaction andseparation of air components in which a first and a second rectifiercolumn is each supplied with top refrigeration for the formation of thereflux necessary for column operation, in which the refrigerant is a gashaving a lower boiling point than nitrogen, in which the bottom of thefirst column collects the oxygen of the air and the bottom of the secondcolumn collects the argon of the air, in which the refrigerant passesfirst thru the second column and then thru the first column, and inwhich the air to be treated, before entering the first column atsubstantially atmospheric pressure, carries reboil heat to the first andthen to the second column bottom.

The process and apparatus described briefly above is hereinafter setforth in detail and illustrated in the accompanying drawings, in which:

The figure is a schematic showing of two rectifier columns embodying thepresent invention and adapted to practice the process of the presentinvention.

In the present disclosure, there is no showing of apparatus or methodfor obtaining refrigeration of the refrig- 3,258,929 Patented July 5,1966 erant used in the columns. The cooling of the refrigerant such asneon, hydrogen, or helium to a temperature below that of the boilingpoint of nitrogen at substantially atmospheric pressure may beaccomplished by any of the prior art methods. The refrigerant may be asingle gas or a combination of gases. The amount of refrigeration, theheat removed from each column, is dependent on the quality and quantityof product to be removed therefrom. The operational drive for a columncomes from the temperature differential between the bottom and the topthereof. This drive is regulated by the amount of heat supplied to thecolumn bottom to evaporate liquid condensed therein and by the amount ofrefrigeration supplied to the top of the column. The heat supplied tothe drive is a function of the amount of reflux, the downward movingcondensate, which, in turn, is a function of the quality and quantity ofthe desired product.

Referring now to the flow of the gas to be separated, air being taken asthe example, atmospheric air is drawn into a turbo-compressor 11 whereit is compressed to approximately 45 p.s.i., after which it is treatedin a treatment plant 12 to remove contaminants such as carbon dioxide,sulphur, and water, and then flows thru conduit 13 and one of two valves14, 15 to one of two precoolers 16, 17. Here the air is cooled to about177 R. (Rankine) by the counter-passage of uncondensed nitrogen leavingthe top of the second 19 of two columns 18, 19, as will later bedescribed. From the precoolers the air passes thru conduit 21 to one oftwo adsorbers 22, 23 that remove any remaining contaminants. The air isthen directed by conduit 24 thru heat exchanger, or reboil, coils 26, 27in series in the columns 18, 19, respectively, air emerging from thelast coil at a temperature of about 163 R. In this connection, liquidoxygen accumulates at the bottom of the column 18 and liquid argon atthe bottom of column 19, as will later appear. This 163 R. air is thenled thru a conduit 28 to and expanded to substantially atmosphericpressure, 25 p.s.i.a., thru an expansion valve 29, and then introducedinto the first, or oxygen, column 18 at substantially the compositionpoint of air in the column, the point 31. The columns 18, 19,respectively, have means (not shown in detail), such as bubble cap trays32, to bring the gas passing upward in the columns and thru the capsinto intimate contact with condensed reflux liquid passing downward,over, and thru the trays therein. The columns 18, 19 are operated atclose to atmospheric pressure. Refrigeration is provided by a cold coil34, condenser coil, at the top of the oxygen column 18 to liquify someof the argon and nitrogen to provide the necessary reflux for the columnoperation. The flow of reflux from the condenser coil 34 to the trays isregulated by a reflux valve 35 below a storage vessel 36, or receiver.Liquid oxygen collects in the bottom of the column "and is removedtherefrom thru a conduit 37 secured to and thru the column bottom.

A saturated vapor mixture of nitrogen and argon flows as overheadproduct from the first column 18 thru a conduit 33 or as a liquid thru avalve 39 to the conduit 38 and then to the second column 19, the argoncolumn, where the mixture is rectified into its argon and nitrogencomponents. The argon-nitrogen feed thru the inlet conduit 38 is to thatportion of the column having the position point of the feed. The argonliquifies and collects in the bottom of the column for removal therefromthru a drain conduit 41 secured to and thru such bottom. A largeproportion of the nitrogen overhead is liquified by a cold coil 42 atthe top of the column and the liquid nitrogen is removed by a conduit43. Condensed nitrogen, also, provides the reflux liquid for the column,and its flow is controlled by a valve 44 fromv a condensate storagevessel 45, or receiver. Uncondensed nitrogen passes as part of theoverhead thru a conduit 46 to the air 3 coolers 16, 17 from which it isexhausted as waste product at substantially ambient temperature.

In each of the rectifier columns 18, 19, heat is supplied at the bottomby the compressed air before it is expanded into the first column 18. Asthe air enters the first column 18, it passes upward thru the trays 32and into intimate contact with the oxygen-argon-nitrogen liquid thereon,which is descending from tray to tray, to give up its oxygen contentthereto. A stream of vapor rises in the column and at each upward stagethe vapor becomes poorer in oxygen and richer in nitrogen and argon,while the descending argon-nitrogen liquid, the reflux, becomes richerin oxygen and leaner in argon and nitrogen. It will be apparent that itdoes not require many stages of successive liquefaction and evaporationto produce a vapor mixture of pure nitrogen and argon at the column topand pure liquid oxygen at the column bottom, provided that thetemperature conditions are such as to tend to bring the ascending vaporinto equilibrium with the liquid at the various stages, or plates, foundnecessary by design and test calculations. The refrigerative effectproducing liquefaction of the argon-nitrogen mixture in the top of thecolumn and of the liquid oxygen which collects in the bottom of thecolumn comes from the cold coil 34, or condenser, in the top of thecolumn,

' which coil acts as a heat sump for the column. The heat exchange coil26 in the bottom of the column transfers heat from the incoming air tothe liquid bottom oxygen to vaporize a portion thereof to provide anupward vapor flow to remove argon and nitrogen from the downwardlymoving liquid. This vaporized oxygen is condensed on the platesthereabove by the descending liquids from thereabove. The temperaturedifferential maintained between the bottom and the top of the columnconstitutes the drive of the column to effect the rectification andcondensation taking place therein. The absolute temperatures maintainedin the column determine the type of products obtained, and the heattransfer rate determines the amount of overhead product obtained withindesign limits.

The operation of the second column 19 is in principle the same as thatof the oxygen column, resulting in the separation of nitrogen and argon,and the production of these gases in liquid form with some gaseousnitrogen passing out thru the overhead conduit 46 leading to the airprecoolers 16, 17. The argon-nitrogen vapor is led from the first column18 into the second column 19 at substantially its composition point,that point in the column having vapor of the same composition. Pureliquid nitrogen condensed in the top of the column 19 by the cold coil42 supplies the reflux liquid which descends thru the column to becomeenriched with argon and to lose nitrogen in the process until at thebottom of the column the liquid is pure argon.

Any of the rare gases which may be present in the air are found with theliquid oxygen or in the vented nitrogen gas, but this does not detractfrom the fact that there is a complete separation of oxygen, argon, andnitrogen by the use of only two rectification columns. Product purity isbetween 99.5% and 99.995 for these gases.

It is to be noted that the flow of refrigerant is first to the secondcolumn 19, the argon column, and then to the first column 18, the oxygencolumn, and that the flow of the input air for heating the columnbottoms is first to the bottom of the first column 18 and then to thebottom of the second column 19. Thus, in the columns the flow ofrefrigerant is counter current to the flow of incoming air as it isbeing precooled by such refrigerant. And, thus, the oxygen column isacted on by the warmer air and refrigerant, and the argon column by thecolder air and refrigerant, which is as it should be as the oxygen hasthe highest boiling temperature of the three gases being condensed andseparated.

4 Having thus described my invention, its construction and operation, Iclaim:

1. A process for the rectification of air to yield oxygen, argon, andnitrogen, that comprises: establishing a first and a secondrectification zone, passing a stream of air in heat exchangerelationship with said first and then said second zone to provide reboilheat for said zones, then passing said stream of air to said first zonefor rectification therein into liquid oxygen product and an overhead ofargon and nitrogen, passing a separate and independent stream ofrefrigerated gas selected from the group consisting of helium, hydrogenand neon in heat exchange relationship with said second zone and thenwith said first zone to provide reflux for said zones, removing saidliquid oxygen and said overhead of argon and nitrogen from said firstzone, introducing said argon and nitrogen overhead to said second zonefor rectification therein to liquid argon product and an overhead ofnitrogen, and removing said liquid argon and said nitrogen overhead fromsaid second zone.

2. A process as defined in claim 1 in which said refrigerated gas isrefrigerated below the temperature of liquid nitrogen at the pressure insaid second zone.

3. A process for separating oxygen, argon and nitrogen from air, thatcomprises: treating the air in a primary rectification zone in such amanner as to produce therein a liquid oxygen product fraction and anargon-nitrogen overhead, transferring said argon-nitrogen overhead to asecondary rectification zone wherein it is treated to produce thereinliquid argon product fraction and a nitrogen overhead, and removing saidliquid argon and nitrogen overhead from said secondary zone; and priorto treating said air in said primary zone, passing it in heat exchangerelationship with said primary zone and then said secondary zone toprovide reboil heat for said zones, and passing a separate andindependent stream of refrigerated gas selected from the groupconsisting of helium, hydrogen and neon, in heat exchange relationshipwith said secondary zone and then said primary zone to provide refluxfor said zones.

4. The combination of claim 3 in which said refrigerated gas isrefrigerated below the temperature of liquid nitrogen at the pressure insaid secondary zone.

5. The method of separating out substantially pure components of oxygen,argon and nitrogen from air which comprises introducing air into a firstrectification zone at substantially the composition point of air in saidzone and at a pressure close to but somewhat above atmospheric pressure,rectifying in said zone to remove liquid oxygen from the bottom thereofsubstantially free of argon and nitrogen and removing argon and nitrogenas overhead from said first zone, passing said argon and nitrogendirectly to a second rectification zone at substantially theircomposition point in said second zone and at a pressure somewhat aboveatmospheric but less than the pressure in said first zone, rectifyingthe mixture of argon and nitrogen to remove liquid argon free ofnitrogen from the bottom of said second zone and nitrogen as overheadfrom said second zone, said nitrogen being removed as overhead from saidsecond rectification zone at a pressure sufiiciently above atmosphericto cause said nitrogen to flow as overhead from said secondrectification zone, and said air being introduced to said firstrectifica 'tion zone at a pressure sufficiently above atmospheric tocause the flow through said first and second rectification zones,refrigerating the top of each of said zones by heat exchange therewithof a separate and independent gas refrigerant selected from the groupconsisting of helium, hydrogen and neon, by passing said gas to saidsecond zone and then to said first zone in series, said gas as it ispassed to said second zone being at a temperature below the temperatureof liquid nitrogen at the pressure in said second zone, and prior tointroduction of said air into the first rectification zone, passing saidair in heat exchange relation with the bottom of said firstrectification zone and then with the bottom of said second rectificationzone to provide reboil heat for said zones.

6. The method of claim 5 in which the liquid oxygen, the liquid argon,and the nitrogen overhead from said second zone are of a purity of 99.5%to 99.995

7. The method for separating out the components of oxygen, argon, andnitrogen from air which comprises introducing air into a firstrectification zone at approximately atmospheric pressure, rectifying insaid zone to remove oxygen as a product from the lower portion of saidzone and a mixture of argon and nitrogen as overhead from said zone,passing said argon and nitrogen to a second rectification zone,rectifying the mixture of argon and nitrogen to remove argon as a.product from the lower portion of said second rectification zone andremoving nitrogen as an overhead product of said second zone, andrefrigerating the top of each of said zones by heat exchange therewithof a separate and independent gas refrigerant selected from the groupconsisting of helium, hydrogen and neon, by passing said gas to saidsecond zone and then to said first zone, said gas as it is passed tosaid second zone being at a temperature below the temperature of liquidnitrogen at the pressure in said second zone, and prior to introductionof said air into the first rectification zone, passing said air in heatexchange relation With the bottom of said first rectification zone andthen with the bottom of said second rectification zone to provide reboilheat for said zones.

8. The method of claim 7 in which the removed oxygen, argon, andnitrogen are of a .purity of 99.5% to 99.995%.

References Cited by the Examiner UNITED STATES PATENTS 815,601 3/1906Linde 6241 1,360,853 11/1920 Wucherer. 1,664,205 3/ 1928 Fonda 6222 X2,240,925 5/ 1941 De Baufre 6222 2,982,106 5/1961 Ambler. 3,037,3596/1962 Knapp 6222 3,062,016 11/ 1962 Dennis 62--22 3,123,457 3/1964Smith 6240 X NORMAN YUDKOFF, Primary Examiner.

1. A PROCESS FOR THE RECTIFICATION OF AIR TO YIELD OXYGEN, ARGON, ANDNITROGEN, THAT COMPRISES: ESTABLISHING A FIRST AND A SECONDRECTIFICATION ZONE, PASSING A STREAM OF AIR IN HEAT EXCHANGERELATIONSHIP WITH SAID FIRST AND THEN SAID SECOND ZONE TO PROVIDE REBOILHEAT FOR SAID ZONES, THEN PASSING SAID STREAM OF AIR TO SAID FIRST ZONEFOR RECTIFICTATION THEREIN INTO LIQUID OXYGEN PRODUCT AND AN OVERHEAD OFARGON AND NITROGEN, PASSING A SEPARATE AND INDEPENDENT STREAM OFREFRIGERATED GAS SELECTED FROM THE GROUP CONSISTING OF HELIUM, HYDROGENAND NEON IN HEAT EXCHANGE RELATIONSHIP WITH SAID SECOND ZONE AND THENWITH SAID FIRST ZONE TO PROVIDE REFLUX FOR SAID ZONES, REMOVING SAIDLIQUID OXYGEN AND SAID OVERHEAD OF ARGON